The present invention relates to an accumulator for use in an air-conditioning system, and more particularly to a suction accumulator for use in an air-conditioning system of a motor vehicle.
Closed-loop refrigeration systems conventionally employ a compressor that is meant to draw in gaseous refrigerant at relatively low pressure and discharge hot refrigerant at relatively high pressure. The hot refrigerant condenses into liquid as it is cooled in a condenser. A small orifice or valve divides the system into high and low-pressure sides. The liquid on the high-pressure side passes through the orifice or valve and turns into a gas in the evaporator as it picks up heat. At low heat loads it is not desirable or possible to evaporate all the liquid. However, liquid refrigerant entering the compressor (known as xe2x80x9cfloodingxe2x80x9d) causes system efficiency loss and can cause damage to the compressor. Hence it is standard practice to include an accumulator between the evaporator and the compressor to separate and store the excess liquid.
An accumulator is typically a metal can, welded together, and often has fittings attached for a switch and/or charge port. One or more inlet tubes and an outlet tube pierce the top, sides, or occasionally the bottom, or attach to fittings provided for that purpose. The refrigerant flowing into a typical accumulator will impinge upon a deflector or baffle intended to reduce the likelihood of liquid flowing out the exit.
There are many inventions of baffles and deflectors in the prior art, all designed to reduce liquid carryover (see for instance U.S. Pat. Nos. 5,787,729, 5,201,792, 5,184,479, 5,021,792, 4,768,355, 4,270,934, and 4,229,949), and the prior art includes designs that claim not to need deflectors (U.S. Pat. Nos. 5,179,844, 5,471,854). However in current standard use most accumulators use a variation of the dome (U.S. Pat. No. 4,474,035) or xe2x80x9cdixie cupxe2x80x9d (U.S. Pat. No. 411,005) deflectorxe2x80x94usually because these are the simplest and most cost-effective.
All deflector designs sacrifice some effective internal volume, as the beginning of the outlet tube must be underneath the deflector. Size is critical in accumulator application, hence there is a need for a more cost-effective design that does not need a deflector.
Some prior art is concerned with reducing the turbulence of the inlet flow (U.S. Pat. No. 5,184,480) as a way to reduce liquid carryover. Other designs are more concerned with the coupling between the inner reservoir and the outlet passage (U.S. Pat. Nos. 5,660,058, 5,179,844, 4,627,247), mainly to reduce the pressure drop across the accumulator (a critical system performance parameter).
The outlet tube is a main feature of accumulators in the prior art. Compressor oil is circulated with the refrigerant in all but very special systems. In systems where compressor oil circulates with the refrigerant the oil will settle out of the stream into the bottom of the liquid reservoir area of the accumulator. Some means must be provided to return this oil to circulation. Much of the prior art is concerned with various tubes, shapes and configurations to accomplish this with the minimum amount of oil inventory left in the accumulator (U.S. Pat. Nos. 5,660,058, 5,778,697, 5,052,193, 4,354,362, 4,199,960). The typical current practice uses a J-shaped outlet tube to carry the exiting gaseous refrigerant from the top of the accumulator down to the bottom and then back up to the outlet from the accumulator. A carefully sized orifice at the bottom of the J-tube entrains the oil from the bottom of the liquid area into the stream of exiting gas. Generally the orifice has a filter around it, and the filter and oil pickup may extend into a sump formed in the bottom of the can to collect the oil.
Another key feature of the prior art is the inclusion of a desiccant in the accumulator. Some refrigerant systems are more susceptible to moisture ingression and damage than others, especially less modern systems. For many systems it is necessary to remove any moisture, and the accumulator is a convenient spot to house the desiccant. Many early designs featured desiccant cartridges and the like (U.S. Pat. Nos. 4,509,340, 4,633,679, 4,768,355, 4,331,001), but the typical modern usage is a fabric bag of some suitable shape, full of desiccant beads and secured to some inner feature of the accumulator (like the J-tube) where the beads will contact the liquid refrigerant.
Another feature typical of the prior art is an anti-siphon measure, which prevents the liquid from siphoning or flowing out of the accumulator reservoir when the system is switched off. Complicated systems have been proposed (U.S. Pat. No. 5,347,829), but the standard technique is a hole near the top of the outlet J-tube to break any siphon effect. The size of the hole is a balance between breaking any siphon and reducing the effectiveness of oil pickup.
A further feature typical of the prior art is the use of insulation placed around the outside of accumulators to modify the thermal characteristics (U.S. Pat. No. 5,701,759). This is an added expense and is only used when required to reduce flooding.
Many examples of prior art (for example U.S. Pat. No. 5,365,751) are proposed as simple, flexible designs that can be easily manufactured for many installations. Since in practice several designs are in use, it is evident that such a multi-purpose design has not been realized in the prior art. An accumulator with reduced number of parts and improved performance is required.
The invention provides an accumulator for use in air-conditioning system comprising: a hermetically sealed outer housing comprising a top, an inlet opening, a peripheral side wall, and a base; an inner liner positioned within said outer housing, said inner liner having a peripheral wall and a base which form a container to receive refrigerant delivered through said inlet opening, said inner liner being spaced from the peripheral wall and the base of said outer housing to define therewith an annular passage, said inner liner having an upper edge that is spaced from said outer housing; passage means extending around the upper edge of said inner liner and communicating the interior of said inner liner with a first upper end of said annular passage; an outlet passage opening from a second lower end of said annular passage at a location between the base of the inner liner and the base of the outer housing, said outlet passage leading to the exterior of said outer housing; the arrangement being such that vaporized refrigerant can pass through said passage means from said inner liner to the upper end of said annular passage, descend downwards through said annular passage to the opening of said outlet passage, and exit said accumulator via said outlet passage.
In one embodiment the outer housing comprises an open topped deep-drawn metal can sealed by a cap through which the inlet opening and an outlet port for the outlet passage extend. In this arrangement the upper edge of the inner liner engages the underside of the cap. The cap preferably is hermetically sealed to the top of the peripheral side wall of the outer housing and may include the inlet opening and also an outlet port for said outlet passage.
Preferably the passage means is formed by a substantially continuous gap between the upper end of the inner liner and the cap, and through this gap refrigerant in gaseous state can pass from the inner container to the annular passage where it can descend between the inner and outer walls to reach the outlet passage at the base. The annular gap is preferably baffled so that it is shielded from passage of liquid refrigerant added to the inner container through the inlet. The passage defined by the annular gap can be configured to create turbulence in the flow of refrigerant gas passing therethrough. The interior of the inner container preferably includes baffles to prevent excessive movement of the refrigerant liquid contained therein. Such a baffle may be provided in the form of a desiccant body positioned in the inner container to take up any water that may be present, the desiccant body preventing liquid refrigerant reaching to the top of the inner container as a result of erratic motion of the accumulator, as can typically occur in automotive installations.
The inner liner preferably includes integral projections on the exterior thereof positioned to engage the outer container and provide a desired spacing therewith.
The inner container is preferably of low thermal conductivity thus to prevent excessive heating of liquid refrigerant therein as a result of heat radiated from the outer container.
There is preferably a bleed hole in the base of the inner container through which accumulated oil can bleed to become entrained in the flow of refrigerant gas moving towards the outlet passage. Preferably rib means between the bases of the inner and outer containers directs such flow in refrigerant gas to pass over the oil bleed passage.
The preferred embodiment of the accumulator for an air-conditioning system as hereinafter disclosed has fewer parts as compared to the prior art, is more effective, and is easier and cheaper to manufacture. It reduces flooding due to greater effective internal volume, better evaporation, an integral baffle, and controlled thermal properties. The inlet fluid separation can be controlled. Further, it has greater control of the amount of compressor oil in circulation, and adjustable coupling between the interior and the outlet passage. It can also accommodate desiccating material in many orientations, and can be made of various materials.
The outer hosing of the accumulator may be of two or more pieces which can be welded, crimped, or otherwise hermetically joined together, and the inner liner has one or more pieces. The outer housing may have various fittings attached for switches, charge ports, or other items. The refrigerant enters the accumulator through an inlet which may be a tube or a hole in the top or side of the outer housing. An inlet tube may be integrally formed or snap-in, or be swaged, brazed, welded or otherwise attached. An inlet hole may be a simple hole or have features formed or machined into it, e.g. a flow director. To direct the flow, reduce turbulence, and/or aid in separating the gaseous refrigerant from the liquid, the inlet may have a diffuser, director, rain hat separator, or flow channellizer attached to, formed with, or held near the inner end. The inlet directs the refrigerant into the inner container formed by the liner. The liquid refrigerant and compressor oil settle to the bottom of the liner where they are contained and insulated from the wall of the outer housing, which may be hot according to the ambient temperature. Hence this arrangement reduces boiling and frothing which might otherwise lead to liquid carryover.
Evaporation of the refrigerant liquids can be controlled by adjusting the thermal connection between the inner liner and the outer housing.
Gaseous refrigerant from the inner container and drawn by the compressor must flow over the top of the inner liner through the annular gap between the liner and the outer housing. This gap may be baffled by features on the outer housing or on the liner, or by separately added pieces. The baffle can reduce the likelihood of liquid refrigerant splashing into the outlet and/or spilling out if the accumulator is tilted.
Furthermore, the peripheral gap can be formed by a plurality of fine holes, or by an attached filter element in order that the refrigerant gas can be filtered as it exits the inner container. The gap may also be sized for optimum flow and/or shaped for optimum coupling between the inner volume and the outlet passage, and may furthermore be designed to impart favourable momentum (e.g. spin) to the exiting refrigerant gas, all with no additional parts or significant additional cost. Since this outlet gap is at the very top of the accumulator the effective internal volume of the accumulator is maximized.
Refrigerant leaving the inner liner must flow down the annular passage between the liner and the outer housing to reach the bottom of the accumulator. The exiting refrigerant is thus in good thermal contact with the outer wall and can pick up heat from the external environment through that wall (which is typically of a good heat conducting material such as aluminium) thus evaporating any liquid refrigerant that may inadvertently have become entrained with the gas. It will be understood that this avoids the above discussed flooding phenomenon.
The outlet passage leading from the bottom of the accumulator towards the exterior may be in the form of a free-standing outlet tube within the liner or attached to an edge thereof, or may even be in thermal contact with the outer housing, again to improve evaporation of any liquid. The discharge end of the outlet tube may be directed out of the top or of the side of the outer housing.
In an alternative configuration wherein discharge from the accumulator is arranged to exit at the bottom thereof, the outlet tube is modified to become a tubular shield closed at its upper end, and within it is coaxially arranged an auxiliary outlet tube having an open upper end leading to an outlet at the bottom of the outer housing. In this arrangement the closed upper end of the tubular shield has a small hole to provide an anti-siphon action.